A flyback converter is used in both alternating current (AC) to direct current (DC) and DC to DC conversion with galvanic isolation between the input and the output. Galvanic isolation and voltage conversion is achieved by a transformer whose primary winding is alternately connected to and disconnected from an input voltage source and whose secondary winding supplies an output voltage to an output capacitor via a rectifying diode. There are two states of a flyback converter in operation. In an on-state, the energy is transferred from the input voltage source to the transformer and the output capacitor supplies energy to an output load. In an off-state, the energy is transferred from the transformer to the output capacitor load and the output load. A common flyback converter as outlined above cannot provide reactive power, i.e., positive voltage with negative current, or negative voltage with positive current, because of the output diode, which blocks the current in one direction.
A bidirectional flyback converter can provide reactive power because the (high-voltage) diode is replaced by a (high-voltage) switch that allows for current flow in both directions. In bidirectional flyback converters, metal oxide semiconductor field-effect transistors (MOSFET) are commonly employed as high-voltage switches. However, high-voltage MOSFETs have higher on-state resistances than those of low voltage MOSFETs and the maximum voltage for high-voltage MOSFETS is 1,000 Volts (V). Therefore, there is a need for an improved high-voltage bidirectional flyback converter with MOSFETs.